Apparatus for generating multiple clock signals of different frequency characteristics

ABSTRACT

A terminal includes at least one wireless communication application module ( 1 ) and a plurality of further application modules ( 4, 5, 6, 8 ). Multiple radio frequency clock signals are generated for the different modules having respective clock frequency characteristics and including at least first and second clock frequencies that are not integral multiples nor sub-multiples of each other nor of a third frequency. The clock generation comprises reference frequency means ( 14 ), fractional-N phase-locked loop frequency synthesizer means ( 15 ) responsive to the reference frequency means, and different automatic frequency control means for adjusting clock frequencies relative to received signals. 
     The reference frequency means ( 14 ) is arranged to supply a common reference frequency signal to a plurality of the fractional-N phase-locked loop frequency synthesizer means ( 17, 18, 19, 25, 26, 41,42 ) that supply the first and second clock frequencies respectively for the application modules. Selective activation means ( 30,52 ) selectively activates and de-activates the phase lock loop means as required by the corresponding application module or modules.

FIELD OF THE INVENTION

This invention relates to clock signal generation and, moreparticularly, to the generation of multiple clock signals of differentfrequency characteristics for portable wireless communication terminalshaving more than one application capability. The term clock signals, asused herein, is to be understood as including sinusoidal, square-waveand other shaped signals defining a frequency and/or phase reference aswell as to pulse clock signals and the term radio frequency is usedherein to refer to frequencies exceeding approximately 1 MHz.

BACKGROUND OF THE INVENTION

End user terminals for wireless communication systems (including radioand television) and portable cellular phones should be small,lightweight and inexpensive and have low power consumption.

The first generation of cellular telephone systems relied on analoguefrequency modulation for speech transmission, and several standards havebeen developed, such as NMT450, NMT900, AMPS, and ETACS. The secondgeneration of cellular systems is based on three different standards: inEurope and some countries in Asia and Australia—Global System For MobileCommunications (GSM), in north America—American Digital Cellular (ADC),and in Japan—Pacific Digital Cellular (PDC). These second generationsystems all employ digital transmission for voice and data, includingsome digital services such as facsimile transmission and short messages.To make the portable terminals smaller and less expensive they makeextensive use of integrated circuits. Most user terminals for 1^(st) and2^(nd) nd generation systems are simple telephone terminals operatingwith a single telephone system and with limited data processingcapability, such as personal data assistants (PDA's—diary, reminder,notebook) and simple games.

A wireless telephone user terminal (or handset) for GSM is described inU.S. Pat. No. 5,493,700, assigned to the assignee of the presentinvention. This user terminal includes a reference frequency generatorcomprising a crystal resonator supplying a fractional-N phase-lockedloop frequency synthesizer, the frequency being corrected bysynchronisation relative to a frequency of the received wirelesscommunication signal.

Communication systems are now being prepared according to a thirdgeneration of standards. Among 3^(rd) generation cellular standards arethe UMTS 3GPP (3^(rd) generation Partnership Project) and 3GPP2standards,of the European Telecommunications Institute (‘ETSI’), theInternational Mobile Telecommunications-2000 (‘IMT-2000’) standards. Itis desirable for the 3^(rd) generation user terminals to be capable offunctioning on at least the local 2^(nd) generation standards as well asthe 3^(rd) generation standards, especially during the period ofintroduction of the 3^(rd) generation and until its coverage is asextensive as the 2^(nd) generation. However, the radio frequency (‘RF’)signals for the two generations are different and are not simple integermultiples or sub-multiples of each other.

In addition, the user terminals for 3^(rd) generation wireless telephonyare inherently capable of adaptation to function with accessories(headsets, printers, or local area networks, for example) and downloadof media (music, speech and video over the Internet) by short-rangewireless communication with the co-operating devices. The personal areanetwork standards, such as BlueTooth, the digital-to-analogue andanalogue-to-digital converters in the audio channels involved, theinclusion of powerful microprocessors and the addition of location awareservices requiring wireless communication with triangulation sources,such as the Global Positioning System (‘GPS’), increase verysignificantly the number of different, high precision radio frequencyclock signals that must be generated and, especially at radiofrequencies, the generation of sufficiently accurate and precise clocksignals tends to be expensive and to have high power consumption levels.

Moreover, the frequency synthesizers used in the wireless transmitterand receiver stages of the different wireless communication applicationsoften need to be synchronised separately relative to the respectivereceived signals by automatic frequency control and the clock signalsused for internal signal processing and data processing need to becontrolled relative to the frequencies used in the transmitter andreceiver stages. In particular, the different radio communication unitsin the terminal, such as GSM and WBCDMA and Bluetooth and GPS, forexample need to be synchronized separately relative to the respectivetypes of base stations, that is to say the GSM Base station, WBCDMA basestation, Bluetooth master unit and GPS satellite master unit, in theseexamples, which are not synchronized between themselves. It is possible,but undesirable for several reasons, to provide separate crystalfrequency references for the respective radio communication units, eachcrystal using its own automatic frequency correction to synchronize tothe respective system networks separately.

The present invention provides an effective relatively lowenergy-consumption means of providing multiple clock frequencies. Theinvention is applicable to wireless telephony and also to otherapparatus where multiple clock frequencies are required.

SUMMARY OF THE INVENTION

The present invention provides apparatus for generating a plurality ofradio frequency clock signals as described in the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block schematic diagram of a portable wireless communicationterminal having several application capabilities, which is not inaccordance with the present invention,

FIG. 2 is a block schematic diagram of a portable wireless communicationterminal having several application capabilities in accordance with oneembodiment of the present invention,

FIG. 3 is a block schematic diagram showing the clock generation of theterminal of FIG. 2 in a mode in which a GSM application in a telephonymodule is active for voice communication and a WBCDMA application in thetelephony module is on standby (monitoring),

FIG. 4 is a block schematic diagram showing the clock generation of theterminal of FIG. 2 in a mode in which the GSM telephony application ismonitoring and the WBCDMA telephony application is active for voicecommunication,

FIG. 5 is a block schematic diagram showing the clock generation of theterminal of FIG. 2 in a mode in which the WBCDMA application is activefor voice and video communication, a video camera and the USB areactive, and a Bluetooth module is active to couple a headset for thevoice communication,

FIG. 6 is a block schematic diagram showing the clock generation of theterminal of FIG. 2 in a mode in which the GSM and WBCDMA telephonymodule is on standby (monitoring), with an organiser (‘PDA’) moduleactive using a USB connection,

FIG. 7 is a block schematic diagram showing the clock generation of theterminal of FIG. 2 in a mode in which the GSM and WBCDMA telephonymodule is on standby, the Bluetooth module is active to couple an MP3player and a stereo (high fidelity) audio coder/decoder is active,

FIG. 8 is a block schematic diagram showing the clock generation of theterminal of FIG. 2 in a mode in which the GSM and WBCDMA telephonymodule is switched off and the PDA module is on standby,

FIG. 9 is a block schematic diagram showing the clock generation of theterminal of FIG. 2 in a mode in which the GSM and WBCDMA telephonymodule, the Bluetooth module and the PDA module are on standby, and

FIG. 10 is a block schematic diagram showing the clock generation of theterminal of FIG. 2 in a mode with only tie PDA module active and withthe Bluetooth module on standby, and

FIG. 11 is a schematic diagram of a multi-accumulator PLL frequencysynthesizer in the terminal of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments of portable wireless communication terminals shown inthe drawings by way of example include a base band wireless cellulartelephony module 1 that processes signals at base band frequencies,adapted for operation on the 2^(nd) generation GSM standard and on the3_(rd) generation WCDMA standard. The terminals also include modules 5and 6 for wireless communication over a personal area network (‘LAN’)with other equipment and accessories in the vicinity, such as a head-setcomprising ear-phones and a microphone, and a printer, for example. Theapplication processor 6 may also provide other functions, such as games,with the possibility of communicating with other terminals. Theterminals also include a GPS module 8 for wireless communication withsatellites of the Global Positioning System to provide positionalinformation. It will be appreciated that the present invention is alsoapplicable to other wireless communication standards.

The embodiments of portable wireless communication terminals shown inthe drawings by way of example also include other modules in wiredconnection, including a video camera 7 and audio coder/decoders(‘Codecs’) 38 and 39.

The power consumptions of the individual modules are substantial and itis important to be able to activate and de-activate, at least partially,the different modules as and when they are needed. The activation andde-activation can be performed manually but, especially in order to beable to provide standby modes in which the modules monitor the arrivalof incoming signals or other events that require full activation of themodules and to shut the modules down at least partially during periodsof inactivity, standby managers 30 and 52 are provided to activate andde-activate the modules automatically.

Referring first to FIG. 1 of the accompanying drawings, the terminalshown, which is not in accordance with the present invention, includes abase band module 1 that processes signals at base band frequencies andco-operates with a receiver and transmitter section (not shown).Frequency synthesisers 2 and 3 generate frequency reference signalsrespectively at 13.0 MHz for GSM communications and at 15.36 MHz forWCDMA communications. A power and audio management module 4 receivesreference frequency signals at the 13.0 MHz or 15.36 MHz frequencies,according to whether communications are occurring in GSM or WCDMAstandard. The terminal also includes a Blue Tooth module 5 forcommunication within a Personal Area Network (‘PAN’) with other devicesand accessories, such as a head-set, a printer, a personal computer, forexample. The terminal also includes an application processor module thatincludes control units (not shown) for controlling the operations of theother modules and that generates a reference frequency signal at 12.0MHz, which it supplies to the Blue Tooth module 5. A video camera 7 alsoreceives the frequency reference signal at 12.0 MHz from the applicationprocessor 6. The terminal also includes a GPS module 8 for receivingsignals from the global positioning system satellites and calculatingpositional information by triangulation.

In order to generate different reference frequencies, the terminalincludes a crystal 9 tuned to 26.0 MHz for the GSM module 2, a crystaltuned to 15.36 MHz for the WCDMA module 3, a crystal 11 tuned to 12.0MHz for the application processor 6, the Blue Tooth module 5, and thecamera 7, and a crystal 12 tuned to 24.5534 MHz for the GPS module 8. Inaddition to these four radio frequency tuned crystals, the terminal alsoincludes a crystal 13 tuned to a substantially lower frequency of 32.768kHz for the power and audio management module 4, the correspondingreference frequency also being supplied to the 3GBB module 1 and theapplication processor 6 for the audio channels.

The use of four radio frequency crystals in the terminal is expensive.In addition, the resulting reference frequencies are not synchronisedrelative to each other and this causes problems when two or more moduleswith different reference frequencies are co-operating together.

FIG. 2 shows a terminal in accordance with a preferred embodiment of thepresent invention, which includes modules whose functions are basicallysimilar to those of the terminal shown in FIG. 1 and that have similarreferences. Thus, the terminal includes a 3G base band processor 1, apower and audio management module 4, a Blue Tooth transmitter/receivermodule 5, an application processor module 6, and a video camera 7. Theterminal also includes a 32.768 kHz crystal 13.

On the other hand, all the radio frequency reference frequencies andother clock signals are derived from a single, common free runningcrystal controlled oscillator (‘VCO’) 14 tuned to 26.0 MHz. The commoncrystal 14 is coupled to a multiple frequency synthesiser and dividermodule 15 that produces several reference frequency outputs with mediumfrequency precision (in this example +/−2 ppm). In order to obtain ahigher degree of frequency precision tolerance, a cellular interfacemodule 16 produces reference frequency signals that are corrected usingautomatic frequency control (“AFC”) derived from the received cellulartelephone signals (GSM or WCDMA) once communication has beenestablished.

In more detail, the frequency synthesiser 15 includes frequencysynthesiser elements 17, 18 and 19 that receive the frequency referencesignal from the common crystal and associated oscillator 14 and producethe appropriate frequencies for reception and transmission in thecellular telephone systems as a function of the actual RF channel number(“ARFCN”) and the AFC signals when available. In particular, thesynthesiser element 17 generates signals for the GSM receiver andtransmitter sections, the synthesiser element 18 generates clock signalsfor the UMTS receiver section and the synthesiser element 19 generatesclock signals for the UMTS and GPRS transmitter sections.

In addition, the frequency synthesiser section 15 includes divider andlow path filter elements 20 to 24 that generate sine wave signalsdirectly from the frequency reference signal from the common crystal andassociated oscillator 14. The divider element 20 generates a sinusoidalsignal at 26 MHz or 13 MHz that is supplied to the cellular interface16, the divider element 21 generates a 26 MHz sinusoidal signal that issupplied to the GPS module 8, the divider element 23 generates a 13 MHzsinusoidal signal that is supplied to the Blue Tooth module 5 and thedivider element 24 generates a 13 MHz sinusoidal signal that is suppliedto the power and audio management module 4. Separate divider and lowpath filter elements are used even where identical frequencies aregenerated, to avoid disturbance to the clock signal supplied to onemodule when a second module using the same frequency is activated orde-activated.

The cellular interface module 16 includes fractional-N PLL frequencysynthesiser elements 25 and 26. The element 25 provides a 13 MHz signalfor the GSM application of the 3G base band processor module 1,corrected by the AFC signal to achieve a more accurate frequencyprecision (±0.1 ppm in this example). The PLL synthesiser 26 convertsthe 13.0 MHz signal from the divider element 20 to 15.36 MHz andcorrects by the AFC signal from WCDMA communication when available. Thesquare wave signals from the cellular interface module 16 are suppliedto the cellular modem processor module 1, where they are used to timethe protocol for frame reception and transmission of the cellulartelephone communications.

The clock signals from the synthesiser elements 25 and 26 are alsosupplied to a multiplexer 27 in the 3G base band processor 1 thatselects the signal corresponding to the mode of operation (GSM or WCDMA)of the processor 1 and supplies the corresponding signal to multiplexers28 and 29 in the power and audio management module 4. The multiplexers28 and 29 also receive the clock signal from the divider element 24 ofthe synthesiser section 15 and the multiplexer 29 also receives the 32kHz signal from the crystal and oscillator 13.

The 3G base band processor 1 and the frequency synthesiser elements 17,18 and 19 of the synthesiser section 15 and 25, 26 of the cellularinterface 16 have relatively high power consumption. Accordingly, inaddition to the full operational mode, in which all these elements arenormally supplied with power, and an “off” mode in which all theseelements are de-activated, so that they are switched off and their powerconsumption is substantially zero, a stand-by or “monitoring” mode isprovided in which the relevant element or elements are activated onlyintermittently to check for the reception of wireless signals, this modebeing controlled automatically or possibly manually by deep sleepmanager elements 30 in the 3G base band processor 1 and 52 in theapplication processor module 6 (to manage the standby modes of the othermodules even when the other deep sleep manager is off. In cellulartelephone operation, when the 3GBB applications are on, the deep sleepmanager 30 or 52 activates the cellular interface 16 and the synthesiserelements 17 to 19. When the 3G applications are off, in the absence ofan activation signal from the processor 1 or 6, the cellular interface16 and the synthesiser elements 17 to 19 are put in battery save mode.In stand-by mode, the deep sleep manager 52 is energised andintermittently activates the cellular interface 16 in response toreceived wireless signals, the synthesiser elements 17 to 19 beingcontinuously activated. In order to enable the Blue Tooth clock signalto be generated for the Blue Tooth module when the 3G applications arenot activated, a further stand-by control signal is generated by a BlueTooth application module 31 in the application processor 6 and appliedto the synthesiser section 15 to enable the crystal and oscillator 14and divider 23 to produce the clock signal for the Blue Tooth module 5.

The processor 1 also generates higher frequency clock signals for adigital signal processor 32 at 170 MHz, a micro controller unit 33 atmore than 95 MHZ and a universal serial bus (“USB”) 34 at 48 MHz. Theprocessor 1, synthesiser section 15 and cellular interface 16 alsogenerate clock signals for internal functions. All these clock signalsare derived ultimately from the common crystal oscillator 14.

In order to supply the USB when the processor 1 is de-activated, a PLLoscillator 35 is provided in the power and audio management module 4 anda PLL oscillator 36 is provided in the application processor 6. A PLLoscillator 37 in the application processor 6 also generates a clocksignal at 200 MHz from the low frequency 32.768 kHz clock signal.

In partial operation, stand-by or enable control signals from theapplication processor can activate and de-activate further elementswithin the synthesiser section 15, and even the reference frequencygenerator 14 including the common RF crystal, to minimise powerconsumption and additionally, the stand-by control signal from the deepsleep manager 30 or 52 may be arranged to activate one only of thesynthesiser elements 25 and 26 and the cellular interface 16 to avoidthe power consumption of both elements when the portable terminal isoperating in a single mode.

The power and audio management module 4 controls the multiplexers 28 and29 to select the source for the clock signal that is applied to acoder/decoder element (“CODEC”) element 37 for voice communication andanother clock signal that is applied to a stereo CODEC (for highfidelity sound) 38. The multiplexer 29 selects the clock signal frommultiplexer 27 to generate an AFC corrected clock signal when operatingin voice mode communication either in GSM or WCDMA or the clock signalfrom divider 24 in the synthesiser 15 which is not AFC when operating inplay back mode from wire connected or internal memory sources or when nocellular telephony application is running. The clock signal from divider24 typically has less than 100 ps of jitter in this example whichenables the PLO 35 to generate a low jitter signal for the stereo CODECat higher frequencies. The multiplexer 28 supplies a cbck signal fromthe multiplexer 27 or the divider 24 to the PLL synthesiser 36 of theapplication processor 6 and the camera 7.

For voice, the following combinations are supported

System Clock Word Clock 13M / 15.36M 8 K

For stereo audio use the following combinations are supported

System Clock Word Clock 13M / 15.36M 48.000 K 13M / 15.36M 44.100 K 13M/ 15.36M 32.000 K 13M / 15.36M 24.000 K 13M / 15.36M 22.050 K 13M /15.36M 16.000 K 13M / 15.36M 12.000 K 13M / 15.36M 11.025 K 13M / 15.36M08.000 K

Also, for the Universal Serial Bus (USB), there is a need to generate aclock at 48 Mhz with a low clock jitter less than 100 ps. This clock isderived also from the clock source 14 and 24. This clock has low jittersince it is directly from the crystal clock 14.

The Blue Tooth module 5 includes a fractional-N PLL frequencysynthesiser that receives a clock signal from divider 23 in thesynthesiser module 15 and to which an AFC correction is applied derivedfrom the signal received from the master terminal in the local areanetwork of the Blue Tooth system, this clock signal being used for thetransmitter and receiver sections. The local area network may include aheadset with earphones used for sound output and a microphone for soundinput and coupled to the power and audio management section. The BlueTooth module may also provide communications with a printer in the localarea network, for example, communicating with a personal digitalassistant (PDA) in the application processor. The Blue Tooth module 5also includes a fractional-N PLL synthesiser 40 that produces a 24 MHzclock signal from the clock signal of divider 23 with AFC to the BlueTooth master station signal, and a divider 41 that derives an 8 MHzclock signal from the output of the synthesiser element 40, the 8 MHzclock signal being supplied to the Blue Tooth application element 31 inthe application processor module 6.

The GPS module 8 includes a fractional-N PLL synthesiser 42 thatproduces a clock signal from the clock signal of divider 21 with AFC tothe received signal from the GPS satellites.

It will be appreciated that all the modules 1, 4, 5, 6, 8, 15 and 16include fractional-N PLL synthesiser elements, the primary referencesignal for which is the common crystal oscillator 14. Each of thesemodules is selectively activated or de-activated, so that the powerconsumption of the frequency synthesiser element associated is onlyincurred when the corresponding application is operational. Differentmodes of partial operation are possible as summarised in the followingtable.

Each synthesizer (17, 18, 19, 25, 26, 41, 42) has the capability toperform digital Automatic frequency correction (AFC) independently toprovide frequency values, the AFC for GSM being different from the AFCfor Bluetooth or for GPS, for example. The use of fractional-N PLLsynthesizers allows high resolution of frequency adjustment for thedigital AFC capabilities.

FIGS. 3 to 10 show examples of clock generation in partial operation ofthe terminal.

In FIG. 3, the GSM application in the cellular telephony module isactive for voice communication and the WBCDMA application is on standby.The reference frequency signal at 26 MHz from the divider 20 is suppliedto the fractional-N PLL synthesizers 25 and 26 in the cellular interfacemodule 16, which supply square wave clock signals at 13 MHz and 15.36MHz respectively to a precision of ±0.1 ppm. The multiplexers 27 and 28select the 13 MHz clock signal for the voice Codec 38. The 32 kHz clocksignal is supplied to the deep sleep manager 52 and the PLL frequencysynthesizer 37 for the micro-controller unit of the applicationprocessor 6.

In FIG. 4, the GSM telephony application is monitoring and the WBCDMAtelephony application is active for voice communication. The referencefrequency signal at 26 MHz from the divider 20 is supplied to thefractional-N PLL synthesizers 25 and 26 in the cellular interface module16, which supply square wave clock signals at 13 MHz and 15.36 MHzrespectively to a precision of ±0.1 pm. The multiplexers 27 and 28select the 15.36 MHz clock signal for the voice Codec 38. The 32 kHzclock signal is supplied to the deep sleep manager 52 and the PLLfrequency synthesizer 37 for the micro-controller unit of theapplication processor 6.

In both the cases of FIGS. 3 and 4, the frequency synthesizers for thestandby telephone application may be energised only intermittently.

In FIG. 5, the WBCDMA application is active for voice and videocommunication, the video camera 7 and the USB 34 are active, and theBluetooth module 5 is active to couple a headset for the voicecommunication. The reference frequency signal at 26 MHz from the divider20 is supplied to the fractional-N PLL synthesizers 25 and 26 in thecellular interface module 16, which supply square wave clock signals at13 MHz and 15.36 MHz respectively to a precision of ±0.1 ppm. Themultiplexers 27 and 28 select the 15.36 MHz clock signal for the voiceCodec 38. The multiplexers 29 selects the 15.36 MHz clock signal for thecamera 7, and the divider 36 for the USB 34. The Blue Tooth module 5receives the reference frequency sine signal from the divider 23 and thedivider 41 supplies the 8 MHz clock signal to the Blue Tooth application31. The 32 kHz clock signal is supplied to the deep sleep manager 52 andthe PLL frequency synthesizer 37 for the micro-controller unit of theapplication processor 6.

In FIG. 6, the GSM and WBCDMA telephony module is on standby(monitoring), with the organiser (‘PDA’) module active using a USBconnection. A standby signal from the deep sleep manager 30 controls theintermittent operation of the cellular interface 16 and the cellularmodem processor 1. The reference frequency signal at 26 MHz from thedivider 20 is supplied to the fractional-N PLL synthesizers 25 and 26 inthe cellular interface module 16, which are intermittently awoken tosupply square wave clock signals at 13 MHz and 15.36 MHz respectively toa precision of ±0.1 ppm. The multiplexer 28 and 29 select the non-AFC 13MHz frequency reference sine signal from the divider 24 for the voiceCodec 38 and for the divider 36 for the USB 34, respectively.

In FIG. 7, the GSM and WBCDMA telephony module is on standby, theBluetooth module is active to couple an MP3 player and the stereo (highfidelity) audio coder/decoder 39 is active. The cellular interface 16and cellular modem processor 1 are awoken intermittently, as in FIG. 6and the Blue Tooth module 5 receives the reference frequency sine signalfrom the divider 23 and the divider 41 supplies the 8 MHz clock signalto the Blue Tooth application 31. The 32 kHz clock signal is supplied tothe deep sleep manager 52 and the PLL frequency synthesizer 37 for themicro-controller unit of the application processor 6.

In FIG. 8, the GSM and WBCDMA telephony module 1 is switched off and thePDA module is on standby. The cellular interface 16 is switched off. Thedeep sleep manager 52 applies a standby signal to awaken the crystalcontrolled oscillator 14 and the divider 24 intermittently. Thefrequency synthesizers 17, 18 and 19 are switched off. The 32 kHz clocksignal is supplied to the deep sleep manager 52 and the PLL frequencysynthesizer 37 for the micro-controller unit of the applicationprocessor 6.

In FIG. 9, the GSM and WBCDMA telephony module, the Bluetooth module andthe PDA module are on standby. The deep sleep manager 52 applies astandby signal to awaken intermittently the crystal controlledoscillator, the cellular interface 16, the frequency synthesizers 17, 18and 19 and the dividers 20, 23 and 24. The 32 kHz clock signal issupplied to the deep sleep manager 52 and the PLL frequency synthesizer37 for the micro-controller unit of the application processor 6.

In FIG. 10, only the PDA module is active and the GSM and WBCDMAtelephony module and the Bluetooth module are on standby. The deep sleepmanager 52 applies a standby signal to awaken intermittently the crystalcontrolled oscillator, the cellular interface 16, the frequencysynthesizers 17, 18 and 19 and the dividers 20, 23 and 24. The 32 kHzclock signal is supplied continuously to the deep sleep manager 52 andthe PLL frequency synthesizer 37 for the micro-controller unit of theapplication processor 6 but only intermittently to the PLL synthesizer32.

The frequency synthesiser elements 17, 18 and 19 may be of the kindincluding multi-accumulator elements as described in U.S. Pat. No.5,493,700. However, in the preferred embodiment of the presentinvention, each of the reference PLL frequency synthesizers 25 and 26 isof the kind shown in FIG. 11, which comprises a voltage-controlledoscillator (‘VCO’) 43, whose output signal is supplied to a frequencydivider 44 that divides the frequency of the VCO by an integer factor Mto obtain the PLL frequency synthesizer output signal. The output signalof the VCO 43 is also supplied to a frequency divider 45 that dividesthe frequency of the VCO by an integer factor N, the frequency divider45 being connected in a feedback loop. The frequency divider 45 includesa multi-accumulator section 46 that enables the factor N to be selectedand to which the digital AFC may be applied. The phase of the outputsignal from the frequency divider 45 is compared with the phase of thefrequency reference from the crystal controlled oscillator 14 in a phasecomparator charge pump device 47. The phase comparator charge pumpdevice 47 supplies resistor-capacitor circuits 48 and 49 that supply acorrection signal to the VCO 43 that is a function of the difference inphase between the signals from the divider 45 and the crystal-controlledoscillator 14.

1. Wireless communication terminal for generating a plurality of radiofrequency clock signals, for use by a plurality of application modulesincluding at least one wireless communication module that comprisestransmitter and receiver means for wireless communication and furtherapplication modules said clock signals having respective clock frequencycharacteristics and including at least first and second clockfrequencies that are not integral multiples nor sub-multiples of eachother nor of a third frequency, said wireless communication terminalcomprising reference frequency means and fractional-N phase-locked loopfrequency synthesizer means responsive to said reference frequencymeans, and automatic frequency control means for adjusting clockfrequencies relative to received signals, wherein said referencefrequency means is arranged to supply a common reference frequencysignal to a plurality of said fractional-N phase-locked loop frequencysynthesizer means that supply said first and second clock frequenciesrespectively for said application modules said wireless communicationterminal comprising selective activation means for selectivelyactivating and de-activating at least one of said plurality of phaselock loop means as required by the corresponding application module ormodules, and at least one of said frequency synthesizer means having asynchronisation value different from the synchronisation value of theother frequency synthesizer means.
 2. Wireless communication terminal asclaimed in claim 1, wherein said frequency synthesizer means includeprogrammable frequency divider means.
 3. Wireless communication terminalof claim 1, wherein said respective clock frequency characteristicsinclude respective clock frequency precision tolerances.
 4. Wirelesscommunication terminal of claim 1, wherein at least one of saidfrequency synthesizer means comprises synchroniser means forsynchronising the corresponding clock signal with a frequency of areceived wireless communication signal, said selective activation meansbeing arranged to activate and de-activate selectively said synchronisermeans and the corresponding application module or modules.
 5. Wirelesscommunication terminal of claim 1, wherein said selective activationmeans is arranged to activate at least one of said frequency synthesizermeans at intervals during a standby phase of the correspondingapplication module.
 6. Wireless communication terminal of claim 1,comprising two of said selective activation means both enabled toactivate the reference frequency sources.
 7. Wireless communicationterminal as claimed in claim 6, wherein said selective de-activationmeans are arranged to de-activate a given reference frequency sourceonly if both of the selective de-activation signal de-activation of thatsource.
 8. Wireless communication terminal of claim 1, wherein saidtransmitter and receiver means includes first and second wirelesscommunication means for wireless communication according to first andsecond standards respectively, said transmitter and receiver means beingresponsive to said first and second clock signals for said first andsecond standards respectively.
 9. Wireless communication terminal asclaimed in claim 8, wherein said first wireless communication meanscomprises a wireless telephony application and said second wirelesscommunication means comprises a data transmission application. 10.Wireless communication terminal of claim 1, wherein at least a secondone of said application modules comprises base-band signal processingmeans for processing signals from more than one other application, saidselective activation means supplying different clock signals to saidbase-band signal processing means depending on the application whosesignals it is processing.
 11. Wireless communication terminal of claim1, and including further reference frequency means defining at least onereference frequency substantially lower than radio frequency and furtherfractional-N phase-locked loop frequency synthesizer means responsive tosaid further reference frequency means said selective activation meansbeing arranged to activate and de-activate selectively said furtherphase lock loop means as required by the corresponding application. 12.Wireless communication terminal as claimed in claim 11, wherein saidfurther reference frequency means is arranged to deliver two outputs,one for said wireless communication module and one for said furtherapplication modules, and wherein said output for said wirelesscommunication module may be disabled or enabled by the applicationprocessor.
 13. Wireless communication terminal for generating aplurality of radio frequency clock signals, for use by a plurality ofapplication modules including at least one wireless communication modulethat comprises transmitter and receiver means for wireless communicationand further application modules, said clock signals having respectiveclock frequency characteristics and including at least first and secondclock frequencies that are not integral multiples nor sub-multiples ofeach other nor of a third frequency, said wireless communicationterminal comprising reference frequency means and fractional-Nphase-locked loop frequency synthesizer means responsive to saidreference frequency means, and automatic frequency control means foradjusting clock frequencies relative to received signals, wherein saidreference frequency means is arranged to supply a common referencefrequency signal to a plurality of said fractional-N phase-locked loopfrequency synthesizer means that supply said first and second clockfrequencies respectively for said application modules said wirelesscommunication terminal comprising selective activation means forselectively activating and de-activating at least one of said pluralityof phase lock loop means as required by the corresponding applicationmodule or modules, and wherein at least one of said frequencysynthesizer means produces a reference frequency without synchronisingthe corresponding clock signal with a frequency of a received wirelesscommunication signal.
 14. Wireless communication terminal as claimed inclaim 13, wherein said frequency synthesizer means include programmablefrequency divider means.
 15. Wireless communication terminal of claim13, wherein said respective clock frequency characteristics includerespective clock frequency precision tolerances.
 16. Wirelesscommunication terminal of claim 13, wherein at least one of saidfrequency synthesizer means comprises synchroniser means forsynchronising the corresponding clock signal with a frequency of areceived wireless communication signal, said selective activation meansbeing arranged to activate and de-activate selectively said synchronisermeans and the corresponding application module or modules.
 17. Wirelesscommunication terminal of claim 13, wherein said selective activationmeans is arranged to activate at least one of said frequency synthesizermeans at intervals during a standby phase of the correspondingapplication module.
 18. Wireless communication terminal of claim 13,comprising two of said selective activation means both enabled toactivate the reference frequency sources.
 19. Wireless communicationterminal as claimed in claim 18, wherein said selective de-activationmeans are arranged to de-activate a given reference frequency sourceonly if both of the selective de-activation means signal de-activationof that source.
 20. Wireless communication terminal as claimed in claim19, wherein said first wireless communication means comprises a wirelesstelephony application and said second wireless communication meanscomprises a data transmission application.
 21. Wireless communicationterminal of claim 13, wherein said transmitter and receiver meansincludes first and second wireless communication means for wirelesscommunication according to first and second standards respectively, saidtransmitter and receiver means being responsive to said first and secondclock signals for said first and second standards respectively. 22.Wireless communication terminal of claim 13, wherein at least a secondone of said application modules comprises base-band signal processingmeans for processing signals from more than one other application, saidselective activation means supplying different clock signals to saidbase-band signal processing means depending on the application whosesignals it is processing.
 23. Wireless communication terminal as claimedin claim 22, wherein said further reference frequency means is arrangedto deliver two outputs, one for said wireless communication module andone for said further application modules, and wherein said output forsaid wireless communication module may be disabled or enabled by theapplication processor.
 24. Wireless communication terminal of claim 13,and including further reference frequency means defining at least onereference frequency substantially lower than radio frequency and furtherfractional-N phase-Locked loop frequency synthesizer means responsive tosaid further reference frequency means, said selective activation meansbeing arranged to activate and de-activate selectively said furtherphase lock loop means as required by the corresponding application.